1. Field of the Invention
The invention relates to the field of cryogenically cooled solid state x-ray detectors. In particular, the invention relates to preventing contamination and icing of the detectors.
2. Related Art
X-ray detectors are maintained and operated at cryogenic temperature, i.e. at the temperature of liquid nitrogen, to retain high performance in energy resolution and low background noise and to extend service life. Most vapors, e.g. moisture, vapors of vacuum pump oils, and decomposed materials from plastics and other packing or insulation materials in the vacuum chamber, can condense and deposit on the detector surface rendering the detector inoperative. These vapors gain access to the detector via openings in the detector holder left to allow insertion of the detector during manufacturing.
Art relating to the development of x-ray detectors includes F. S. Goulding and J. M. Jaklevic, "Photon-excited Energy-dispersive X-ray Fluorescence Analysis for Trace Elements", Annual Review of Nuclear Science, Vol. 23, 1973, pp. 45-74; N. W. Madden, et al., "An Improved Operating Mode for a Si(Li) X-ray Spectrometer", IEEE Transactions on Nuclear Science , Vol. 37, 1990, pp. 171-176; and F. S. Goulding et al., "Detector Background and Sensitivity of Semiconductor X-ray Fluorescence Spectrometers", Advances in X-ray Analysis, Vol. 15, 1972, pp. 470-482.
Currently, when the cleanliness of the detector environment becomes questionable, various methods are used to prevent contamination. These include: a mechanism to retract the detector when it is not in use; thermal energy to drive off contaminants (see e.g. U.S. Pat. No. 4,931,650); placing the detector in a deeply recessed holder; and enclosing the whole body of the detector holder. These designs compromise performance or are costly.
To achieve best performance, the detector must be placed within a few millimeters of the sample of interest to increase sensitivity and solid angle of detection. Any extra enclosures around the detector holder increase the distance between the detector and the sample.